Evidence that a kinesin is associated with ectoplasmic specializations in the testis

During spermatogenesis, spermatids undergo a “down and up” translocation event in the seminiferous epithelium. This event has been proposed to be microtubule‐based and to result from the movement of apical “ectoplasmic specializations” (adhesion junctions) along adjacent Sertoli cell microtubule tracts. Dynein is present at the junctions and is likely responsible for the upward movement of spermatids. A kinesin is likely responsible for the downward movement of spermatids. To test the hypothesis that a kinesin is associated with the junctions, we generated an antibody to the “LAGSE” sequence conserved amongst kinesins, and reacted the antibody with fixed frozen sections of epithelium or fixed epithelial fragments. In tissue processed for immunofluorescensce, the antibody reacted at sites known to contain apical ectoplasmic specializations, in addition to reacting with other structures in the epithelium known to contain kinesins. In material processed for immunogold localization, the antibody reacted with the cytoplasmic face of the endoplasmic reticulum component of ectoplasmic specializations. Kinesin mRNA transcript screens using mouse GeneChip arrays of testis and Sertoli cells indicated that a possible candidate kinesin for spermatid translocation is Rab6KIFL. Antibodies generated against a peptide sequence that is unique to this kinesin reacted with regions associated with spermatid heads, and with a band on immunoblots that is not present in other tissues and migrates at a higher molecular weight than that known for Rab6KIFL. We are currently identifying the protein. Our results are consistent with the prediction that a kinesin is associated with ectoplasmic specializations. CIHR MOP 62768